Shortest path tree and minimum-spanning tree, Computer Networking

We studied Dijkstra's link-state routing algorithm for computing the unicast paths that are individually the shortest paths from the source to all destinations. The union of these paths might be thought of as forming a shortest path tree. If each links has an associated cost and the cost of a tree is the sum of the link costs, then a spanning tree whose cost is the minimum of all of the spanning trees is called a minimum spanning tree. Both shortest path tree and minimum-spanning tree can be used for broadcast routing. By constructing a counterexample, show that the least-cost path tree is not always the same as a minimum spanning tree.